I used it a few years back, but for me the color temperatures never scaled right. I like my lights at 4500-5500K during the day, but it looks a little too warm on my monitor (f.lux defaults daylight to 6500K.) Maybe it's my lights/monitor, but I really wish I could set different curves, or at least different color temperature targets for my lights and monitor. f.lux didn't allow me to do that. It only gives options for "warmer" and "a lot warmer," which both look weird at night. I ultimately hacked something else together, but it was a little disappointing, because I really like f.lux.